KR102279925B1 - liquefaction system of boil-off gas and ship having the same - Google Patents

Abstract

The present invention relates to a BOG reliquefaction system and a ship, comprising: a liquefied gas storage tank; a compressor for compressing the boil-off gas of the liquefied gas storage tank; a pressure reducing valve for reducing the compressed boil-off gas; a gas-liquid separator for separating the flash gas from the depressurized boil-off gas; and a flash gas storage tank for storing the flash gas.

Description

BOG reliquefaction system and ship {liquefaction system of boil-off gas and ship having the same}

The present invention relates to a boil-off gas reliquefaction system and a ship.

According to recent technology development, liquefied gas such as liquefied natural gas (Liquefied Natural Gas) and liquefied petroleum gas (Liquefied Petroleum Gas) is widely used to replace gasoline or diesel.

Liquefied natural gas is liquefied by cooling and liquefying methane obtained by refining natural gas collected from a gas field. It is a colorless and transparent liquid with few pollutants and high calorific value. On the other hand, liquefied petroleum gas is a fuel made into a liquid by compressing the gas containing propane (C3H8) and butane (C4H10) together with petroleum from oil fields at room temperature. Liquefied petroleum gas, like liquefied natural gas, is colorless and odorless and is widely used as fuel for household, business, industrial, and automobile use.

Such liquefied gas is stored in a liquefied gas storage tank installed on the ground or stored in a liquefied gas storage tank provided in a ship that is a means of transportation to navigate the ocean. The volume of liquefied petroleum gas is reduced to 1/260 of propane and 1/230 of butane by liquefaction, which has the advantage of high storage efficiency. The temperature and pressure required to drive the engine using the liquefied gas as fuel may be different from the state of the liquefied gas stored in the tank.

In addition, when LNG is stored in liquid form, some of the LNG is vaporized and boil off gas (BOG) is generated as heat penetration occurs into the tank, and such boil-off gas may cause problems in the BOG re-liquefaction system. In this case, it was attempted to solve the problem by discharging BOG to the outside and specifically burning it (in the past, BOG was simply discharged to the outside to remove the risk of damage to the tank by lowering the tank pressure). It causes problems of pollution and waste of resources.

Therefore, in recent years, as a technology for efficiently processing BOG, utilization measures such as re-liquefying the generated BOG and supplying it to the engine have been made. Since this has not been done, continuous research and development are being made on this.

The present invention was created to solve the problems of the prior art as described above, and an object of the present invention is to efficiently maintain the pressure of the liquefied gas storage tank by decompressing and re-liquefying boil-off gas, and to effectively control excess boil-off gas. It is to provide a BOG reliquefaction system and a ship that can.

BOG reliquefaction system according to an embodiment of the present invention, a liquefied gas storage tank; a compressor for compressing the boil-off gas of the liquefied gas storage tank; a pressure reducing valve for reducing the compressed boil-off gas; a gas-liquid separator for separating the flash gas from the depressurized boil-off gas; and a flash gas storage tank for storing the flash gas.

Specifically, the flash gas storage tank may adsorb and store the flash gas using an adsorbent.

Specifically, it may further include a boil-off gas heat exchanger for heat-exchanging the boil-off gas generated in the liquefied gas storage tank with the compressed boil-off gas.

Specifically, the boil-off gas heat exchanger may exchange heat with the boil-off gas generated in the liquefied gas storage tank, the compressed boil-off gas, and the flash gas.

Specifically, the BOG heat exchanger may include: a low pressure BOG flow path through which BOG generated in the liquefied gas storage tank flows; a high-pressure boil-off gas passage through which the compressed boil-off gas flows; and a flash gas flow path through which the flash gas flows.

Specifically, the BOG heat exchanger may include: a low pressure BOG flow path through which BOG generated in the liquefied gas storage tank flows; and a high-pressure boil-off gas flow path through which the compressed boil-off gas flows.

Specifically, it may further include a flash gas heat exchanger for exchanging the depressurized boil-off gas with the flash gas.

Specifically, a boil-off gas supply line connected from the liquefied gas storage tank to a consumer, the compressor is provided, and passes through the low-pressure boil-off gas flow path of the boil-off gas heat exchanger; a boil-off gas liquefaction line branched from the boil-off gas supply line and provided with the b pressure reducing valve and passing through the high-pressure boil-off gas flow path of the boil-off gas heat exchanger; and a boil-off gas return line connected from the gas-liquid separator to the liquefied gas storage tank and transferring the re-liquefied gas separated in the gas-liquid separator to the liquefied gas storage tank.

Specifically, the gas-liquid separator may further include a flash gas delivery line connected to the flash gas storage tank and passing through the flash gas flow path of the boil-off gas heat exchanger.

Specifically, a boil-off gas supply line connected from the liquefied gas storage tank to a consumer, the compressor is provided, and passes through the low-pressure boil-off gas flow path of the boil-off gas heat exchanger; a boil-off gas liquefaction line branched from the boil-off gas supply line and provided with the pressure reducing valve and sequentially passing through the high-pressure boil-off gas flow path of the boil-off gas heat exchanger and the flash gas heat exchanger; and a boil-off gas return line connected from the gas-liquid separator to the liquefied gas storage tank and transferring the re-liquefied gas separated in the gas-liquid separator to the liquefied gas storage tank.

Specifically, the gas-liquid separator may further include a flash gas delivery line connected to the flash gas storage tank and passing through the flash gas heat exchanger.

Specifically, it may further include a flash gas supply line connected from the flash gas storage tank to the consumer.

Specifically, the adsorbent may be at least one selected from activated carbon, activated carbon fiber, carbon nanotube, zeolite, and MOF.

Specifically, the flash gas storage tank may have an internal pressure of 5 bar to 40 bar, which is a preset pressure range.

Specifically, the flash gas storage tank may have a temperature of -50 degrees to 25 degrees, which is a preset temperature range.

A ship according to an embodiment of the present invention is characterized in that it has the boil-off gas reliquefaction system.

The BOG reliquefaction system and the vessel according to the present invention reduce the BOG pressure and reliquefy it and store the flash gas separately, thereby preventing a decrease in the reliquefaction efficiency and reducing BOG generated in the liquefied gas storage tank. By discharging it, it has an advantageous effect on maintaining the pressure of the liquefied gas storage tank.

1 is a conceptual diagram of a BOG reliquefaction system according to a first embodiment of the present invention.
2 is a conceptual diagram of a BOG reliquefaction system according to a second embodiment of the present invention.

The objects, specific advantages and novel features of the present invention will become more apparent from the following detailed description and preferred embodiments taken in conjunction with the accompanying drawings. In the present specification, in adding reference numbers to the components of each drawing, it should be noted that only the same components are given the same number as possible even though they are indicated on different drawings. In addition, in describing the present invention, if it is determined that a detailed description of a related known technology may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Hereinafter, the BOG reliquefaction system of the present invention will be described, and the present invention includes a BOG reliquefaction system and a ship having the same.

Hereinafter, in this specification, liquefied gas may be used to encompass all gas fuels that are generally stored in a liquid state, such as LNG or LPG, ethylene, ammonia, etc. can be expressed as This can be applied to boil-off gas as well. In addition, for convenience, LNG can be used to encompass both NG (Natural Gas) in a liquid state as well as NG in a supercritical state, etc., and BOG can be used to mean not only gaseous BOG but also liquefied BOG. there is.

In addition, hereinafter, the decompression may be a state generated through expansion, and conversely, since the decompression may be a state generated by the expansion, the decompression and the expansion may be used interchangeably.

1 is a conceptual diagram of a BOG reliquefaction system according to a first embodiment of the present invention.

1, the BOG reliquefaction system 1 according to the first embodiment of the present invention includes a liquefied gas storage tank 10, a compressor 20, a pressure reducing valve 30, a gas-liquid separator 40, It includes a flash gas storage tank 50 and a boil-off gas heat exchanger 60 .

The liquefied gas storage tank 10 stores the boil-off gas (generated by natural vaporization of the liquefied gas stored in the liquefied gas storage tank 10) to be supplied to the consumer 100 . The liquefied gas storage tank 10 should store the liquefied gas in a liquid state. At this time, the liquefied gas storage tank 10 may store the liquefied gas at a pressure of 1 bar to 10 bar (eg 1.03 bar).

Here, the consumer 100 receiving the boil-off gas of the liquefied gas storage tank 10 is a high-pressure engine (ME-GI engine, etc.) using a high-pressure gas such as 200 bar to 400 bar (for example, 300 bar), 1 bar to 50 bar, etc. It includes low-pressure engines (XDF, DFDE, DFDG, etc.), boilers, GCUs, turbines, etc. that use low or medium pressure gas. In the present invention, the consumer 100 may be used to encompass all configurations that consume BOG.

The liquefied gas storage tank 10 may be of a stand-alone type, a membrane type, a pressurization type, etc., and may use various insulating structures to store the liquefied gas in a liquid state, and evaporation occurring in the liquefied gas storage tank 10 may be used. The gas may be processed by a compressor 20 or the like, which will be described later.

The compressor 20 compresses the boil-off gas generated in the liquefied gas storage tank 10 . BOG compressed by the compressor 20 may be supplied to the consumer 100 or may be transferred to the pressure reducing valve 30 to be reliquefied.

The compressor 20 is provided in plurality and may be, for example, five stages, and the demand 100 may be connected to the downstream of the five-stage compressor 20 or the downstream of the two-stage compressor 20 according to the required pressure. In addition, a cooler 21 is provided downstream of each compressor 20 to cool the boil-off gas heated by the compression heat.

A boil-off gas supply line 22 may be provided from the liquefied gas storage tank 10 to the consumer 100 , and a valve (not shown) for controlling the supply amount of boil-off gas, a compressor 20 , may be provided in the boil-off gas supply line 22 . ) can be provided.

The boil-off gas supply line 22 may be provided to pass through the low-pressure boil-off gas flow path 61 of the boil-off gas heat exchanger 60 to be described later, and the boil-off gas flowing along the boil-off gas supply line 22 is a boil-off gas heat exchanger. After being preheated in ( 60 ), it may be introduced into the compressor ( 20 ).

In case the BOG generated in the liquefied gas storage tank 10 does not meet the required flow rate of the consumer 100, a mixer (not shown) is provided in the BOG supply line 22, and the liquefied gas storage tank A liquefied gas supply line (not shown) may be connected from the liquefied gas pump (not shown) installed in 10 to the mixer, and a forced vaporizer (not shown) may be provided on the liquefied gas supply line. In this case, the shortfall in BOG may be supplemented by forcibly vaporized liquefied gas.

The pressure reducing valve 30 depressurizes the boil-off gas. The BOG liquefaction line 31 may be branched from the BOG supply line 22 , and the pressure reducing valve 30 may be provided in the BOG liquefaction line 31 . At this time, the BOG liquefaction line 31 may pass through the high-pressure BOG flow path 62 of the BOG heat exchanger 60 .

The pressure reducing valve 30 may be provided downstream of the boil-off gas heat exchanger 60 in the boil-off gas liquefaction line 31 . Accordingly, the pressure reducing valve 30 may at least partially liquefy the boil-off gas of high pressure heat-exchanged in the boil-off gas heat exchanger 60 to 1 to 10 bar. When the pressure is sharply decreased, the temperature is also decreased, so that the boil-off gas whose pressure is rapidly dropped by the pressure reducing valve 30 may be liquefied.

The pressure reducing valve 30 may be a Joule-Thomson valve using the Joule-Thomson effect, and of course, an expander (not shown) may be provided instead of the pressure reducing valve 30 . may be

The pressure reduction valve 30 may control the pressure reduction according to the internal pressure of the liquefied gas storage tank 10 , and the pressure reduction pressure by the pressure reduction valve 30 may be maintained higher than the inner pressure of the liquefied gas storage tank 10 . This is to easily return the re-liquefied gas from the gas-liquid separator 40 to the liquefied gas storage tank 10 .

The gas-liquid separator 40 separates the flash gas from the boil-off gas cooled in the boil-off gas heat exchanger 60 and liquefied by pressure reduction in the pressure reducing valve 30 . The gas-liquid separator 40 may separate the boil-off gas into a gas component (flash gas) and a liquid component (reliquefaction gas).

The boil-off gas liquefaction line 31 is branched from the boil-off gas supply line 22 in the downstream of at least one of the plurality of compressors 20 and is connected to the gas-liquid separator 40, the gas-liquid separator 40 A boil-off gas return line 41 for returning the liquid component to the liquefied gas storage tank 10 may be connected to the lower end of the .

On the other hand, a flash gas delivery line 42 is provided at the upper end of the gas-liquid separator 40 . The flash gas delivery line 42 may be connected from the gas-liquid separator 40 to the flash gas storage tank 50 via the flash gas flow path 63 of the boil-off gas heat exchanger 60 .

At this time, the flash gas delivery line 42 is connected to the flash gas storage tank 50 via the flash gas flow path 63 of the boil-off gas heat exchanger 60 , so that the flash gas is high-pressured in the boil-off gas heat exchanger 60 . After heat exchange with the boil-off gas of the boil-off gas and the boil-off gas of low pressure, it may be introduced into the flash gas storage tank 50 .

The gas-liquid separator 40 may be provided with a configuration for regulating the internal pressure, and for example, a configuration for heating the boil-off gas introduced into the gas-liquid separator 40 may be provided. When the boil-off gas introduced into the gas-liquid separator 40 is heated, the internal pressure of the gas-liquid separator 40 may increase.

Raising the internal pressure of the gas-liquid separator 40 is that the internal pressure of the gas-liquid separator 40 is sufficiently higher than the pressure of the liquefied gas storage tank 10 so that re-liquefied gas, which is a liquid component, smoothly enters the liquefied gas storage tank 10 without a pump. in order to be returned. At this time, the internal pressure of the gas-liquid separator 40 may be maintained at 2 to 6 bar, which is a pressure higher than that of the liquefied gas storage tank 10 .

The flash gas storage tank 50 stores flash gas. The flash gas, which is a gas component separated in the gas-liquid separator 40 , may be stored in the flash gas storage tank 50 after exchanging heat with the high-pressure BOG and the low-pressure BOG in the BOG heat exchanger 60 .

In this embodiment, in the process of re-liquefying the boil-off gas under reduced pressure, if complete re-liquefaction occurs, flash gas may not be generated. However, since nitrogen contained in boil-off gas has a very low boiling point of -190 degrees or less, the nitrogen component may remain without being liquefied only by depressurization.

At this time, the flash gas having a high nitrogen component ratio may be separated from the gas-liquid separator 40 , and the reliquefied gas having a low nitrogen component ratio may be returned to the liquefied gas storage tank 10 . Therefore, the nitrogen component ratio in the liquefied gas storage tank 10 in the liquefaction process can be lowered.

The flash gas separated in the gas-liquid separator 40 may be stored in the flash gas storage tank 50 and then supplied to the demand 100 , where the demand 100 is the boil-off gas by the boil-off gas supply line 22 . It may be a demand source 100 receiving a supply.

To this end, the flash gas supply line 51 may be connected from the flash gas storage tank 50 to the consumer 100 . In this case, the flash gas supply line 51 may be directly connected to the demand source 100 or may be joined to the boil-off gas supply line 22 , and the consumer 100 to which the flash gas is supplied may be a low pressure demand source 100 . there is.

Of course, the customer 100 to which the flash gas supply line 51 is connected may be different from the customer 100 to which the boil-off gas supply line 22 is connected. The demand 100 to which the gas supply line 51 is connected may be a gas combustion unit (GCU).

The flash gas storage tank 50 may adsorb and store the flash gas using an adsorbent. When the gas in the present invention is natural gas, the flash gas storage tank 50 may store Absorbed Natural Gas (ANG). At this time, the adsorbent may be at least one selected from activated carbon, activated carbon fiber, carbon nanotube, zeolite, and MOF, and may be a variety of materials that adsorb and store flash gas. The flash gas adsorbed and stored in the flash gas storage tank 50 may be desorbed from the adsorbent and supplied to the consumer 100 .

When the flash gas storage tank 50 stores the flash gas using an adsorbent, the storage capacity may vary depending on the temperature. That is, since the flash gas can be more adsorbed to the adsorbent when the temperature is low, the storage capacity of the flash gas storage tank 50 can be increased when the temperature is lowered.

On the other hand, when the temperature increases, since the flash gas is about to be desorbed from the adsorbent, the storage capacity of the flash gas storage tank 50 may be reduced. In this embodiment, when the flash gas is desorbed from the adsorbent and supplied to the consumer 100 by using this point, various waste heat generated in the ship can be utilized. For example, the flash gas storage tank 50 may promote desorption of the flash gas by utilizing heat (heat of combustion, exhaust heat, etc.) generated from the consumer 100 connected to the flash gas supply line 51 .

In addition, in the flash gas storage tank 50, when the pressure increases, the storage capacity of the flash gas may increase, and when the pressure decreases, the storage capacity of the flash gas may decrease. In order to use this, the pressure reducing valve 30 may control whether or not to depressurize the boil-off gas in consideration of the internal pressure of the flash gas storage tank 50 .

To this end, a pressure gauge (not shown) may be provided in the flash gas storage tank 50 , and the pressure reducing valve 30 may control the pressure reduction range of the boil-off gas in consideration of a value measured by the pressure gauge.

For example, when the pressure reducing valve 30 increases the pressure of the boil-off gas, the pressure of the flash gas is lowered, so the storage capacity of the flash gas storage tank 50 may be reduced, but on the other hand, the reliquefaction efficiency of the boil-off gas according to the pressure reduction. this can be higher

Conversely, when the pressure reducing valve 30 reduces the pressure of the boil-off gas, the pressure of the flash gas increases, so the storage capacity of the flash gas storage tank 50 may increase, but on the other hand, the reliquefaction efficiency of the boil-off gas according to the decompression may decrease. can

That is, the reliquefaction efficiency of boil-off gas and the storage capacity of the flash gas storage tank 50 may change in inverse proportion to each other according to the pressure reduction range by the pressure reducing valve 30 . Of course, since the amount of flash gas is reduced when the reliquefaction efficiency is increased, there is no problem even if the storage capacity of the flash gas storage tank 50 is reduced.

However, in this embodiment, the pressure reducing valve 30 is configured such that the storage capacity of the flash gas storage tank 50 is greater than or equal to the reference value for the operation of the consumer 100 connected to the flash gas storage tank 50, and the flash gas It is possible to adjust the pressure reduction while considering the internal pressure of the storage tank (50).

Of course, in the present embodiment, it may be possible to implement a change in the storage capacity of the flash gas storage tank 50 through the internal pressure control in the gas-liquid separator 40 together with or separately from the pressure reduction control by the pressure reducing valve 30 .

That is, the pressure reduction by the pressure reducing valve 30 and the internal pressure control of the gas-liquid separator 40 may affect the storage capacity of the flash gas storage tank 50, and at the same time affect the amount of flash gas generated (reliquefaction efficiency). go crazy However, since the boiling point of the BOG increases as the pressure increases, the reliquefaction efficiency is considered when the boiling point that varies depending on the temperature is taken into account even if the cooling of the BOG by the decompression is actually reduced due to the reduced pressure by the pressure reducing valve 30 . may not be significantly reduced.

Therefore, without significantly reducing the reliquefaction efficiency, the pressure reducing valve 30 and the gas-liquid separator 40 adjust the pressure of the flash gas (regulating it above the reference value) to adjust the storage capacity in the flash gas storage tank 50 . can

The flash gas stored in the flash gas storage tank 50 may be higher than the pressure of the liquefied gas and the boil-off gas stored in the liquefied gas storage tank 10 . This is because the internal pressure of the gas-liquid separator 40 may be formed higher than the internal pressure of the liquefied gas storage tank 10 .

Therefore, when the flash gas supply line 51 connected to the flash gas storage tank 50 is joined to the boil-off gas supply line 22, in consideration of the pressure of the flash gas, at least one of the compressors 20 downstream ( upstream of the remaining compressor 20).

When the compressor 20 provided in the BOG supply line 22 is operated with too low a load (load of about 10 to 30% or less), the driving stability deteriorates, the compression efficiency is lowered, and the power consumption compared to the BOG flow rate is excessive. As can be done, in this embodiment, the flash gas is mixed upstream of the compressor 20 in the boil-off gas supply line 22 to maintain the load of the compressor 20 above a certain level, thereby stably and efficiently maintaining the compressor 20 . can be operated with

Also in this case, considering that the temperature of the flash gas is lower than the temperature of the boil-off gas compressed in the compressor 20 , the cooler 21 may be omitted at the point where the flash gas is joined in the boil-off gas supply line 22 . . For example, when the flash gas supply line 51 is connected downstream of the first compressor 20 , a cooler may be omitted between the first compressor 20 and the second compressor 20 .

That is, the flash gas supply line 51 joins the flash gas into the boil-off gas supply line 22 according to the request of the consumer 100, or as the load of the compressor 20 decreases, the flash gas is transferred to the boil-off gas supply line (22) can be combined.

This means that the load of the compressor 20 can be used to adjust the pressure reduction range of the pressure reducing valve 30 or the internal pressure of the gas-liquid separator 40 . When the load of the compressor 20 falls below the reference value, in order to deliver the flash gas to the compressor 20 to raise the load on the compressor 20, the pressure reducing valve 30 is increased and the internal pressure of the gas-liquid separator 40 is lowered. can

Of course, in addition to the control of the pressure reducing valve 30 and the gas-liquid separator 40, a gas discharge line (not shown) that may be provided in the flash gas storage tank 50 may be used, and when the gas discharge line is opened, the flash gas is stored As the internal pressure of the tank 50 is naturally lowered toward atmospheric pressure, desorption of the flash gas may be performed.

The flash gas storage tank 50 may maintain a preset pressure range and a preset temperature range. At this time, the flash gas storage tank 50 may have an internal pressure of 5 bar to 40 bar, which is a preset pressure range, and may have a temperature of -50 degrees to 25 degrees, which is a preset temperature range.

Of course, the numerical values of the preset pressure range and the preset temperature range are not limited to the above, but the flash gas storage tank 50 can maintain the internal pressure and temperature to properly maintain the storage of the flash gas, and Maintenance can be implemented by manipulation of the components described in the present invention.

The boil-off gas heat exchanger 60 heats the boil-off gas generated in the liquefied gas storage tank 10 with the boil-off gas compressed in the compressor 20 . To this end, the BOG heat exchanger 60 includes at least a low-pressure BOG flow path 61 through which BOG generated in the liquefied gas storage tank 10 flows, and a high-pressure BOG flow path 62 through which compressed BOG flows. It may have a structure having two flow paths.

In the BOG heat exchanger 60 , the BOG supply line 22 is connected to the low pressure BOG flow path 61 , and the BOG liquefaction line 31 is connected to the high pressure BOG flow path 62 . Accordingly, the boil-off gas heat exchanger 60 flows the high-pressure boil-off gas flowing toward the pressure reducing valve 30 along the boil-off gas liquefaction line 31 toward the compressor 20 along the boil-off gas supply line 22 . It can be cooled with low-pressure boil-off gas.

Since the high-pressure BOG is compressed by the compressor 20 and received compression heat, it may be at a higher temperature than the low-pressure BOG discharged from the liquefied gas storage tank 10 . Accordingly, the high-pressure BOG may be cooled while exchanging heat with the low-pressure BOG in the BOG heat exchanger 60 and then introduced into the pressure reducing valve 30, thus increasing the reliquefaction efficiency.

In addition, since low-pressure BOG is preheated by the BOG heat exchanger 60 and then flows into the compressor 20, it may not be necessary to provide the compressor 20 with specifications that can withstand cryogenic temperatures. That is, in the present embodiment, the compressor 20 may use the room temperature compressor 20 .

The boil-off gas heat exchanger 60 may heat-exchange the flash gas with the high-pressure boil-off gas and the low pressure boil-off gas. That is, the boil-off gas heat exchanger 60 may exchange heat exchange between the boil-off gas generated in the liquefied gas storage tank 10, the compressed boil-off gas, and the flash gas, and for this purpose, it may have a flash gas flow path 63 through which the flash gas flows. there is.

The boil-off gas heat exchanger 60 may have a structure having three independent flow paths, and the flash gas flow path 63 may be connected to a flash gas delivery line 42 . The flash gas is separated from the gas-liquid separator 40 and flows into the flash gas flow path 63 of the boil-off gas heat exchanger 60 along the flash gas delivery line 42 , and is mixed with high-pressure, high-temperature boil-off gas and low-pressure, low-temperature boil-off gas. heat exchange is possible.

At this time, the flash gas may be used to cool the boil-off gas at high pressure and high temperature, and after being slightly heated, it may be stored in the flash gas storage tank 50 through the flash gas delivery line 42 .

However, as described above, since the storage capacity of the flash gas storage tank 50 may change depending on the temperature of the flash gas, the flash gas delivery line 42 connects the flash gas flow path 63 of the boil-off gas heat exchanger 60 . It may be provided to be at least partially bypassed, and the flash gas bypasses the boil-off gas heat exchanger 60 in the flash gas delivery line 42 , the storage capacity of the flash gas storage tank 50 and variables related thereto The flow rate can be controlled according to the

For example, since the high-pressure boil-off gas is cooled by heat exchange with the flash gas, reliquefaction efficiency can be secured even if the pressure reducing valve 30 reduces the pressure for reliquefaction. In this case, since the pressure of the flash gas is increased, even if the flash gas is heated while exchanging heat in the boil-off gas heat exchanger 60 , the storage capacity of the flash gas storage tank 50 can be sufficiently secured.

As described above, in this embodiment, the BOG is liquefied by reducing the pressure, and by storing the flash gas separated from the reliquefied BOG, the internal pressure is effectively increased as BOG is generated in the liquefied gas storage tank 10 . can be suppressed

2 is a conceptual diagram of a BOG reliquefaction system according to a second embodiment of the present invention.

Referring to FIG. 2 , the BOG reliquefaction system 1 according to the second embodiment of the present invention may further include a flash gas heat exchanger 70 compared to the first embodiment.

Hereinafter, the present embodiment will be mainly described on the points that are different from the first embodiment, and the parts omitted from the description will be replaced with the previous ones.

In this embodiment, the pressure reducing valve 30 may be provided in two or more. The plurality of pressure reducing valves 30 may be respectively provided before and after the boil-off gas heat exchanger 60 . At this time, the boil-off gas that has been primarily decompressed may be introduced into the high-pressure boil-off gas flow path 62 of the boil-off gas heat exchanger 60 .

The pressure reducing valve 30 provided downstream of the boil-off gas heat exchanger 60 may be provided to adjust the internal pressure of the gas-liquid separator 40 . That is, the pressure reducing valve 30 between the gas-liquid separation and the boil-off gas heat exchanger 60 may hold the pressure in the gas-liquid separator 40 .

The pressure reducing valve 30 between the gas-liquid separation and the boil-off gas heat exchanger 60 is a measured value (internal pressure of the liquefied gas storage tank 10) of a pressure gauge (not shown) that can be installed in the liquefied gas storage tank 10 . ), the internal pressure of the gas-liquid separator 40 can be adjusted. In this case, since the pressure of the gas-liquid separator 40 is sufficiently high, when the re-liquefied gas, which is a liquid component, is returned to the liquefied gas storage tank 10 through the boil-off gas return line 41 in the gas-liquid separator 40 , a separate pump may be omitted.

It goes without saying that the configuration in which a plurality of pressure reducing valves 30 are provided as described above can also be applied to the first embodiment.

The flash gas heat exchanger 70 heats the decompressed boil-off gas with the flash gas. The flash gas may be provided on the BOG liquefaction line 31 , and may be provided downstream of the BOG heat exchanger 60 in the BOG liquefaction line 31 .

In the present embodiment, the BOG heat exchanger 60 may have a two-channel structure having a high-pressure BOG flow path 62 and a low pressure BOG flow path 61, and the BOG compressed at high pressure is a BOG heat exchanger. At 60 , it may be cooled by the low-pressure boil-off gas discharged from the liquefied gas storage tank 10 , and may be further cooled by the flash gas in the flash gas heat exchanger 70 .

Between the gas-liquid separator 40 and the boil-off gas heat exchanger 60 , the flash gas may be provided upstream of the pressure reducing valve 30 . Therefore, the BOG compressed by the compressor 20 may be cooled in two stages in the BOG heat exchanger 60 and the flash gas heat exchanger 70 and then liquefied as the pressure is reduced.

A flash gas delivery line 42 may pass through the flash gas heat exchanger 70 . As described above, the flash gas delivery line 42 does not pass through the flash gas heat exchanger 70 , but at least a portion of the flash gas It may have a structure to bypass the heat exchanger 70 , and the flow rate at which the flash gas bypasses the flash gas heat exchanger 70 may be controlled by factors such as the storage capacity of the flash gas storage tank 50 . .

In the present embodiment, a gas combustion device 90 may be further provided to prevent the internal pressure of the liquefied gas storage tank 10 from excessively rising, and from the liquefied gas storage tank 10 to the gas combustion device 90 . A gas combustion line 91 may be connected.

At this time, in this embodiment, a safety valve (not shown) is provided in the gas combustion line 91 , and as the safety valve is opened according to the internal pressure of the liquefied gas storage tank 10 , the liquefied gas storage tank 10 . When the internal pressure of the BOG is automatically discharged through the gas combustion line 91, it can be burned in the gas combustion device 90.

Of course, in the present invention, the gas combustion device 90 and the like in the present embodiment described above can also be applied to the first embodiment. That is, a combination of the first embodiment and the second embodiment also falls within the scope of the present invention.

Although the present invention has been described in detail through specific examples, this is for the purpose of describing the present invention in detail, and the present invention is not limited thereto, and by those of ordinary skill in the art within the technical spirit of the present invention. It will be clear that the transformation or improvement is possible.

All simple modifications and variations of the present invention fall within the scope of the present invention, and the specific scope of protection of the present invention will become clear from the appended claims.

1: BOG reliquefaction system 10: Liquefied gas storage tank
20: compressor 30: pressure reducing valve
40: gas-liquid separator 50: flash gas storage tank
60: boil-off gas heat exchanger 70: flash gas heat exchanger
100: demand

Claims (16)

liquefied gas storage tank;
a compressor for compressing the boil-off gas of the liquefied gas storage tank;
a pressure reducing valve for reducing the compressed boil-off gas;
a gas-liquid separator for separating the flash gas from the depressurized boil-off gas; and
and a flash gas storage tank for storing the flash gas,
The flash gas storage tank has a characteristic that when the pressure increases, the storage capacity of the flash gas increases, and when the pressure decreases, the flash gas storage capacity decreases,
The pressure reducing valve adjusts whether the BOG is reduced in consideration of the internal pressure of the flash gas storage tank so that the storage capacity of the flash gas storage tank is greater than or equal to a reference value. According to claim 1, wherein the flash gas storage tank,
BOG reliquefaction system, characterized in that the flash gas is adsorbed and stored using an adsorbent. The method of claim 1,
BOG reliquefaction system, characterized in that it further comprises a BOG heat exchanger for heat-exchanging BOG generated in the liquefied gas storage tank with the compressed BOG. According to claim 3, wherein the boil-off gas heat exchanger,
BOG reliquefaction system, characterized in that heat exchange between the boil-off gas generated in the liquefied gas storage tank and the compressed boil-off gas and the flash gas. According to claim 4, wherein the boil-off gas heat exchanger,
a low-pressure boil-off gas passage through which the boil-off gas generated in the liquefied gas storage tank flows;
a high-pressure boil-off gas passage through which the compressed boil-off gas flows; and
BOG reliquefaction system, characterized in that it has a flash gas flow path through which the flash gas flows. According to claim 3, wherein the boil-off gas heat exchanger,
a low-pressure boil-off gas passage through which the boil-off gas generated in the liquefied gas storage tank flows; and
BOG reliquefaction system, characterized in that it has a high-pressure BOG flow path through which the compressed BOG flows. 7. The method of claim 6,
BOG reliquefaction system further comprising a flash gas heat exchanger for exchanging the depressurized BOG with the flash gas. 6. The method of claim 5,
a boil-off gas supply line connected from the liquefied gas storage tank to a consumer, the compressor being provided and passing through the low-pressure boil-off gas flow path of the boil-off gas heat exchanger;
a boil-off gas liquefaction line branched from the boil-off gas supply line and provided with the pressure reducing valve and passing through the high-pressure boil-off gas flow path of the boil-off gas heat exchanger; and
The BOG reliquefaction system further comprising a BOG return line connected from the gas-liquid separator to the liquefied gas storage tank and transferring the reliquefied gas separated in the gas-liquid separator to the liquefied gas storage tank. 9. The method of claim 8,
BOG reliquefaction system, further comprising a flash gas delivery line connected from the gas-liquid separator to the flash gas storage tank and passing through the flash gas flow path of the boil-off gas heat exchanger. 8. The method of claim 7,
a boil-off gas supply line connected from the liquefied gas storage tank to a consumer, the compressor being provided and passing through the low-pressure boil-off gas flow path of the boil-off gas heat exchanger;
a boil-off gas liquefaction line branched from the boil-off gas supply line and provided with the pressure reducing valve and sequentially passing through the high-pressure boil-off gas flow path of the boil-off gas heat exchanger and the flash gas heat exchanger; and
The BOG reliquefaction system further comprising a BOG return line connected from the gas-liquid separator to the liquefied gas storage tank and transferring the reliquefied gas separated in the gas-liquid separator to the liquefied gas storage tank. 11. The method of claim 10,
BOG reliquefaction system, further comprising a flash gas delivery line connected from the gas-liquid separator to the flash gas storage tank and passing through the flash gas heat exchanger. The method of claim 1,
Further comprising a flash gas supply line connected to the flash gas storage tank,
The compressor consists of multiple stages,
The flash gas supply line, BOG reliquefaction system, characterized in that connected to the downstream of at least one compression stage and upstream of the other compression stage in the compressor. According to claim 2, wherein the adsorbent,
BOG reliquefaction system, characterized in that at least one selected from activated carbon, activated carbon fiber, carbon nanotube, zeolite and MOF. According to claim 1, wherein the gas-liquid separator,
The boil-off gas reliquefaction system, characterized in that the storage capacity of the flash gas storage tank is greater than or equal to a reference value by adjusting the internal pressure along with the pressure reduction of the boil-off gas by the pressure reducing valve. According to claim 1, wherein the flash gas storage tank,
BOG reliquefaction system, characterized in that it has a temperature of -50 degrees to 25 degrees, which is a preset temperature range. A ship characterized in that it has the boil-off gas reliquefaction system according to any one of claims 1 to 15.

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